1. Field of the Invention
The present invention relates to a drive apparatus for moving a certain object (driven object) in a desired direction.
2. Description of the Prior Art
An example of the prior art having this type of drive apparatus is the XY drive apparatus indicated in FIG. 1. As indicated in FIG. 1, said XY drive apparatus is comprised of X table 1 installed on the floor or a mounting frame in a workplace, and Y table 2 moved by said X table 1. Furthermore, as X table 1 and Y table 2 mutually have nearly the same constitution, the following explanation will be provided with respect to X table 1 only, with an explanation of Y table 2 omitted. However, those constituent members of Y table 2 that correspond to the constituent members of X table 1 are indicated using the same reference numerals. Furthermore, an exploded view of the constituent members of X table 1 divided into suitable sections is indicated in FIG. 2.
As indicated in FIG. 1, X table 1 has rectangular plate-shaped base 5, and side plate 6, provided on said base 5 and forming a box with said base 5. Motor 7 is mounted on one end of this side plate 6. In addition, as is indicated in FIG. 2, pulley 9 is fit onto output shaft 7a of motor 7. In addition, another pulley 10 is arranged on base 5, and is mounted to base 5 by means of brackets not shown. A belt-shaped member in the form of endless belt 12, in this case a flat steel belt, is wrapped around pulleys 9 and 10. A driven object in the form of moving table 13 is attached to this belt 12.
As indicated in the drawings, moving table 13 has a prescribed thickness and is composed to be of a size that allows it to be contained within the width of side plate 6. Two table projections 13a projecting above the upper surface of side plate 6 are provided in parallel on the left and right sides. These table projections 13a may be formed into an integrated structure with moving table 13 or may be composed in the form of separate structures. Above-mentioned Y table 2 is mounted on the upper surface of said table projections. Furthermore, cover 15 is arranged to the inside of these table projections 13a, acting to prevent entrance of dust and so on.
A driving device that drives the belt-shaped member in the form of belt 12 is comprised of the above-mentioned motor 7, pulley 9 and pulley 10. In addition, the drive apparatus, which moves the driven object, moving table 13, by applying a driving force, is comprised of said drive device and belt 12.
On the other hand, as is indicated in FIG. 2, a pair of linear motion rolling guide units 17 are mutually arranged in parallel on the right and left sides beneath the above-mentioned drive apparatus, and are mounted on base 5. These linear motion rolling guide units 17 receive the load in all four directions (the directions indicated by arrows Z and Y as well as their respective opposite directions) applied to moving table 13, and also act as guiding devices that guide moving table 13.
This linear motion rolling guide unit 17 is comprised of track rail 18, roughly in the shape of a square column, in which circular ball track rail groove 18a is formed in the left and right shoulders of the side wall, slider 20, having a cross-section roughly in the shape of the letter "U", in which circular ball track rail groove 20a is formed in opposition to ball track rail groove 18a of track rail 18, and flat plate-shaped retainers (not shown), arranged at equal intervals in the sliding direction between ball track rail grooves 18a and 20a, and holding the ball while allowing rotation. Furthermore, linear motion rolling guide units 17 are not limited to the use of a ball, but may also use other devices such as a roller as long as they are of a constitution that uses a rolling object.
The following provides an explanation of the operation of the XY table having the above-mentioned constitution. Furthermore, as X table 1 and Y table 2 have the same constitution as described above, the following explanation will concentrate on X table 1.
Firstly, when a power voltage is supplied to motor 7 of X table 1, output shaft 7a of motor 7, serving as the driving source, rotates which transmits torque to pulley 9. Then, belt 12 wrapped around pulley 9 and pulley 10 is driven in a prescribed direction, and moving table 13 mounted on the upper surface of this belt 12 also moves in the same direction. Conversely, when the direction of rotation of motor 7 is reversed, belt 12 is driven in the opposite direction from that above, and consequently, moving table 13 also moves in that direction. In addition, the movement of moving table 13 is controlled by a control circuit comprised of a microcomputer and so on. A detector, which outputs a position detection signal to this control circuit, is composed to be able to be mounted to the inside of side plate 6 indicated in FIG. 1, and on the upper surface of base 5. In addition, detection may also be performed by an encoder mounted behind motor 7.
In addition, since Y table 2 is mounted on table projections 13a of moving table 13 equipped on X table 1, it moves in the X direction which is the same direction as moving table 13 of X table 1. As moving table 13 of Y table 2 is independently composed so as to be able to move linearly in the Y direction, by controlling these with a control circuit not shown, moving table 13 of Y table 2 can be moved in both the X and Y directions.
As described above, the drive apparatus of the prior art equipped with an XY table is composed so that a driving force from motor 7 is transmitted by means of pulley 9 to belt 12 by simply belt 12 being directly coupled to a driven object in the form of moving table 13. For this reason, the driven amount of belt 12 and the movement amount of moving table 13 are the same. Thus, this drive apparatus of the prior art has the shortcoming of it being difficult to position moving table 13 at a desired stopping position with a high degree of accuracy in consideration of the inertia of the weight of moving table 13 and a loaded object and so on. In addition, in this constitution in which belt 12 and moving table 13 are coupled directly, as a result of the entire weight of Y table 2 and a workpiece, etc., loaded on said Y table 2 being applied to moving table 13 of X table 1, there is the risk of the torque of motor 7 of X table 1 being insufficient with respect to this increase in the weight load, thereby preventing Y table 2 from moving on X table 1.